Sunday, May 13, 2007


Steve's "Otter Of The Week"! Karl E. Hayes

The Otter is a great airframe, and a "turbine" seemed a "perfect match". Otter N3904 (54) was tested by Western Rotorcraft of Seattle in 1972 with a Garrett AiResearch TPE-331 engine but the project did not proceed and the aircraft had its radial engine re-installed. In or about 1975, as a result of customer pressure, DHC did look at a turbo Otter project and considered re-engining existing Otters as well as production of new aircraft. It appears however that they were never very enthusiastic about the project, realising that the price of the finished product would be very high, probably too high for the market. They were also influenced by their Turbo Beaver, which with sales of only 60 aircraft was not considered a great commercial success. They decided not to proceed. Along came "Ray Cox"!


The next exponent of the Turbo Otter was Cox Air Resources of Edmonton, Alberta, a company formed by Mr. Ray Cox to develop the aircraft. He was an aircraft mechanic and pilot, with many years experience in the Arctic. Since 1969 he had specialised in recovering crashed aircraft from remote locations, with more than fifty to his credit. His idea came from extensive work with Otters in the Arctic. He appreciated that they were a fine aircraft, with hardly any life limit to the airframe, but also realised that the Otter would eventually be driven into retirement by the economics of the operation and maintenance of its piston engine. He saw the solution to the problem with the P&W PT-6A-27 turboprop, the engine which powered the DHC-6 Twin Otter.

He teamed up with an aeronautical engineer named Aimo Pitkanen and set about designing and building a Turbo Otter. They saw their aircraft as the only replacement for the piston engined Otter, and as there was no-one else working on such a proposal, saw themselves in a “no competition” situation. Their aircraft would (a) reduce maintenance costs and the number of engine replacements (b) achieve greater productivity through higher cruising speed and increased payload, with improved crew and passenger comfort through decreased noise levels and (c) overcome any problems of availability of 80/87 avgas by changing to jet turbo fuel, as well as (d) increase utilization and profitability. This increased profitability (which would be achieved by lower expenditure on maintenance man hours, longer Time Between Overhauls, greater payload for short hauls, higher cruising speed, improved climb characteristics making operations in restricted areas safer and more profitable) would appeal to the bush operators, and there were a considerable number of Otters still operating in Canada which were likely candidates for conversion. They received enquiries from many parts of the world, as well as from Canada, which convinced them of the need for such a conversion, which they estimated to cost 200,000 Canadian dollars in 1977. It was considered that at the very least 40 aircraft would be converted, which would give them an extra ten to fifteen years service at competitive operating costs.

The Otter chosen as the prototype turbo conversion was number 421, which had been delivered to McMurray Air Services in 1961 as CF-MES. It was subsequently sold to Gateway Aviation of Edmonton. On 24th August 1973 it met with a bad accident at Cambridge Bay, Northwest Territories as a result of engine failure and was officially classified as “destroyed”. This however overlooked Ray Cox's considerable talents at salvaging and restoring aircraft. It was brought back to Edmonton and rebuilt as the prototype Cox Turbo Otter. Many problems were encountered during the conversion, mostly to do with weight and balance. The 42 gallon rear tank was relocated forward of the bulkhead, under the cockpit floor. A new 40 gallon hopper tank was installed forward of the firewall, which helped solve the centre of gravity problem caused by the much lighter engine up front, and which would sustain flight for one hour in the event of electrical systems failure.

The powerplant was the Pratt & Whitney PT-6A-27 turbine, developing 662 shp and driving a four bladed Hartzell 109.5 inch diameter propeller, which was fully reversible for water and land use and could be locked in zero-thrust configuration for engine starts on water. This would greatly improve the Otter's water-handling characteristics. A new electrical system was installed and a new instrument panel. As the avionics would be to each individual customer's requirements, racking was provided to accommodate whatever systems were required. A standard package was prepared incorporating state-of-the-art navigation and communications equipment.

The Turbo Otter was envisaged as being able to operate with the same wheel, float and ski arrangements as the standard Otter. The aircraft would have the same gross weight as the Otter (8000 pounds) but empty weight would be reduced by approximately 700 pounds, thus enabling increased payloads to be carried over 100 nautical mile ranges. Projected cruising speed was 125 knots with wheels (116 knots with floats), range 750 nautical miles, endurance six hours and a rate of climb one thousand feet per minute. These details were announced at a press conference held in Edmonton in November 1977. The prototype was to have flown in September 1977, but the project was delayed and funding proved problematical. As its own resources were inadequate, the company had to find external financing. This is a difficult matter at the best of times but none of the conventional sources would consider an unproved concept such as the Turbo Otter. The project did however continue with assistance from the Alberta Opportunities Corporation, the provincial lending agency.

By the time the prototype, registered C-FMES-X, made its first flight from Edmonton on 26th September 1978, more than a million dollars had been invested in the programme. Certification was expected to follow shortly thereafter, at which stage a plant was to be opened at Vegreville near Edmonton, to convert Otters at a rate of 18 per year. However, despite the successful first flight, continued funding for the Canadian certification became impossible to obtain, and the operation was moved south of the border. A new company, Cox Aircraft Corporation, continued with the work, based at Renton Airport, Seattle, Washington. The Turbo Otter was placed on the US civil aircraft register as N4247A in June 1981, and was tested with a higher powered PT-6A-135. US and Canadian certification was undertaken in parallel. Both engines would be on offer, the higher powered PT-6A-135 appealing to the hot-and-high operator.

According to a magazine interview in April 1982, the company's president Ray Cox said that it had received to that date 30 orders for the conversion from commercial operators. He added that there had also been considerable interest in the performance improvements from military operators of the Otter. To quote from the article, which appeared in Aviation Week & Space Technology magazine: “Cox's timetable for starting the conversion program depends on obtaining the required financing, but under current plans the first Otter with a PT-6A-27 engine is scheduled for completion in September 1982. Cox estimates it will take 90 days to produce the next two re-engined Otters, and then the Renton facility should be able to accomplish each conversion in 30 days. Three to five aircraft could be converted in the facility at any one time”.

“The $410,000 conversion price for the Otter includes the PT-6A-27 engine, zero timing the airframe and new electrical and fuel system components. Updated avionics would also be included in the standard package. Options being offered at an additional price include a larger cargo door, an additional two windows and three passenger seats and a leading-edge wing fuel tank. The eleven to fourteen passenger Cox conversion without the optional fuel increases the range of the aircraft to 750 miles with reserves. Cox says he has received expressions of interest from operators in South America, India, Kenya and Germany”.

As well as the prototype Cox Turbo Otter, number 421, Cox also acquired Otter number 126, which was intended as the second conversion. It was damaged in a crash at Lynn Lake, Manitoba in May 1976 but was transported to Seattle to be rebuilt. Otter number 158 was intended as the third conversion. A former US Navy aircraft, it had been transported to Calgary in January 1981, where it was worked on by Kimba Air Services prior to going by road to Seattle for the turbo conversion. In the event, that never happened, and the aircraft was destroyed in a hangar fire in Calgary in May 1983. Otter number 380, a former RCAF aircraft which had crashed, was also acquired by Mr Cox with a view to being converted to turbine power as soon as certification was achieved.

The certification of the Cox Turbo Otter proved to be a lengthy one, and the prototype was still engaged in test flying when disaster struck the project on 19th December 1984. On that day, N4247A crashed at Alki Point, five miles from Boeing Field, Seattle, where by that stage the project was based. No one was killed in the crash, but the Otter came down in a residential neighbourhood and was badly damaged. The wreck of the Otter was brought back to Boeing Field. The Cox Turbo Otter project had always been somewhat under-funded, and it never recovered from this set-back. The
following month, January 1985, the aircraft was re-registered to the Cox Aircraft Company of Washington Inc, Seattle but was not repaired. It had never achieved certification and the project had run out of luck, and money. It was a sad end indeed after so much money and effort had been put into the venture.

All information is from Karl Hayes' "masterful" CD entitled:

De Havilland Canada


Otter 421

Otter 421 was delivered to McMurray Air Services Ltd of Uranium City, Saskatchewan on 26th May 1961 registered CF-MES. It was the company's third Otter, following CF-JXR (202) and CF-LAP (289), and it replaced JXR which had been lost in an accident on 29th April 1961 while engaged in supporting the Polar Continental Shelf Project (PCSP). Immediately after delivery, MES headed north to support the PCSP, taking over from JXR, based at Isachsen in the High Arctic. An incident was recorded on 30th April 1962, MES then operating from the Decca Green Station on Brock Island, still engaged on PCSP duties. The Otter made a forced landing at a point ten miles from Cape Murray as a result of a failed cylinder. The engine was repaired and the Otter returned to service the same day.

McMurray Air Services eventually lost the PCSP contract to Bradley Air Services, and in October 1969 was taken over by Gateway Aviation Ltd of Hangar 13, Industrial Airport, Edmonton. The three Otters then operated by McMurray Air Services, CF-ITS (90), CF-LAP (289) and CF-MES (421) were registered to Gateway Aviation on 21st October 1969 and entered service with Gateway Aviation, primarily in the Northwest Territories. Otter MES was used to support a NASA geological expedition to the True North Pole, with John Cameron as pilot and Ray Cox as Flight Engineer. MES continued to fly for Gateway Aviation until an accident on 24th August 1973. The Otter had taken off from Cambridge Bay en route to a fishing camp. It was flying below a one thousand foot ceiling when the engine failed due to fuel contamination, and the Otter force landed in rough gravel terrain at position 69.10 North 107.02 West. The engine broke away from the airframe and there was extensive damage to the wings, fuselage and floats. According to the accident report, the aircraft was “destroyed”.

Despite the severity of the crash, the occupants were uninjured and walked to the fishing camp three miles away. Alouette helicopter CF-QCV was in the vicinity and relayed the 'Mayday' call from the Otter. Cessna 180 CF-NYO attempted to go to the rescue, but was unable due to adverse weather. Gateway arranged for Northward Aviation Twin Otter CF-JCH to pick up the passengers and return them to Cambridge Bay. It was unable to do so that day due to weather obscured, one quarter mile visibility in light rain and fog, but completed the rescue the following day. That was the end of the Otter's career with Gateway Aviation. It became the property of the insurers, who sold it to Fred H.Ross & Associates of Edmonton, who on 4th December 1974 sold it on to Mr Ray Cox for $6,500, who had flown with the Otter while a flight engineer with Gateway Aviation. He retrieved it from the accident site and brought it back to Edmonton.

Ray Cox had been working on a project to convert the Otter to turbine power, and set about rebuilding MES as the prototype of the Cox Turbo Otter, complete with a PT-6 turbine engine. On completion of the re-build, the Otter was registered CF-MES-X to Cox Air Resources Inc, Hangar 3, Municipal Airport, Edmonton in April 1977 and commenced test flying, with a view to achieving certification of the turbine conversion. The Otter was noted at the Canadian Armed Forces base at Cold Lake, Alberta during December 1978. Efforts at achieving certification continued for some years, and by May 1981 the project had been relocated from Edmonton to Renton Airfield, Seattle. In June 1981 the Otter was registered N4247A to Cox Aircraft Corporation, Renton. The project was later moved from Renton to Boeing Field, Seattle. The certification process proved a lengthy one, and the Otter was still engaged on test flying when an accident occurred on 19th December 1984 at Alki Point, five miles from Boeing Field.

To quote from the accident report: “The aircraft was performing test flight manoeuvres when problems with the modified fuel system occurred. Ice blocking a fuel vent line caused a partial collapse of the main (engine feed) fuel cell, which produced an erroneous fuel quantity reading. In addition, the main tank overflow shut-off valve was leaking, so tank over-flow occurred. The fuel overflow caution light illuminated and the auxiliary tank fuel pump feed to the main tank automatically shut down. Due to mis-calibration, this system over-rode the pilot's attempts to re-start the auxiliary fuel pumps. The pilot remained in the test area, troubleshooting, rather than making an immediate return to base, noting that the main tank gauge continued to read full. En route to Boeing Field, fuel starvation occurred. The pilot opted to attempt a forced landing in a small sports field in a residential area rather than ditching in the Puget Sound. The aircraft touched down in the intended landing area, then bounced across an adjacent street. The arresting action of telephone wires on the vertical fin brought the aircraft to rest in a residential backyard”.

There were three on board the aircraft. Pilot Hal Joines (61) and an instrumentation engineer were uninjured. There was also a flight engineer who sustained a leg injury. Some further details from the Seattle Post-Intelligencer newspaper: “I've bailed out a few times, but this is the first time I ever crashed", said veteran pilot Joines, clad in blue coveralls, relaxed and easygoing as he talked with reporters near the crash scene. We had been working over the Olympic Peninsula for about an hour, testing anti-icing mechanisms of the engine, and were headed back to Boeing Field when we began to get a loss of fuel pressure and the engine quit at 1,500 feet over Alki Point. I feathered the prop and was trying to make a wide street (Alki Avenue SW) but there was too much traffic. I saw the Bar-S Ball Field and tried to make an emergency landing there, but I overshot. We were going too fast and we hit the power lines and the garage roof. I'm depressed. We lost an airplane, a good airplane”.

The newspaper described the scene: “The airplane's tail wheel was resting on a garage, and the nose was stuck in the back yard at 3053, 64th Avenue SW. One wing of the blue and white aircraft hung over the alley, the other touched the house. The rudder assembly was hanging from utility wires in a front yard about 50 yards away. The top branches of a nearby tree were shredded where the aircraft had passed between the ground and other utility wires”. The wrecked Otter was taken to Boeing Field, where it languished for months, being subsequently moved to Arlington Airport north of Seattle. The month after the crash, in January 1985, the Otter was re- registered to Cox Aircraft Company of Washington Inc. Sadly however this crash marked the end of the Cox Turbo Otter, which despite an immense effort by Mr Ray Cox over the years, had run out of luck, and money.

The crash had an interesting sequel in the courts. The “residential backyard” where the Otter had come to rest belonged to a Mr.Douglas Crosby, who had to spend $3,199-89 in repairs to his garage roof. He sued Cox Aircraft Company of Washington and on 4th November 1985 the Superior Court for King County, Washington entered judgement in his favour, holding that Cox Aircraft Company was strictly liable for the damages. In other words, as Mr Crosby clearly had done nothing wrong, he was entitled to recover his damages regardless of other considerations from the owners of the Otter which had caused the damage. Under normal circumstances, any person claiming damages would have to prove that the person he sued was guilty of negligence before he could recover damages, but the judge ruled this was not necessary in this case.

Although the amount of money involved was small, there was an important point of legal principle involved, whether a person on the ground who suffered damage from an aircraft, even one on a test flight, was entitled to recover damages automatically, or did that person have to prove that the operator of the aircraft was negligent before he could recover damages. In this case, Mr Crosby had not proved any negligence on the part of the Cox Aircraft Company, who appealed to a higher court. In cases such as this, involving important points of principle, other interested parties are allowed make arguments. Mr.Crosby was supported by the Washington Trial Lawyer's Association, who were all in favour of the strict liability argument, in other words, no proof of negligence required. On the other hand, Cox Aircraft Company was supported by the Boeing Company, who strongly argued that the liability of aircraft owners and operators for ground damage should be governed by a negligence standard. The appeal was heard by the Supreme Court of Washington State in December 1987, who decided in favour of the Cox Aircraft Company. Otter N4247A had certainly made its mark on the law, clarifying this important legal point.

- by Karl E. Hayes

Ray, you had a "great idea", which today is "manifested in the "Vazar" and "Walter" and "Texas Turbine" Otter engine conversions. "Great thinking"!


Iknow Ray Cox, I participated in a small why in his engine conversion project. We were also interested in the recovery of the P-38s in Greenland. Ray if you read this,e mail me. this is Alex Strong
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